HIV on the brain

Researchers find that the ability of HIV to cause dementia may be an example …

HIV infections are primarily noted for symptoms such as a depleted immune system and a severe wasting. But up to 50 percent of the untreated cases can result in an HIV triggered dementia and sensory problems. These neural defects contribute significantly to the virus's lethality. The virus appears to only be capable of invading neural tissue during the period of primary infection, however, and doesn't always wind up invading the brain.

There have been some results that suggest that the invasion of the central nervous system by HIV may represent a classic case of evolutionary adaptation. The brain and the rest of the body represent very different environments, both in terms of immune activity and cells present. As such, the ability of HIV to invade the CNS may depend on HIV's ability to adapt to that environment. That, in turn, may depend on heritable genetic changes in the HIV genome. As a possible prelude to specifically blocking the invasion of the brain, an international group of researchers started looking at whether specific changes in the HIV genome correlated with the ability of the virus to attack the brain.

I probably wouldn't be writing about this if they hadn't found them. By comparing virus isolated from cerebro-spinal fluid to that found in the blood plasma of the same patient, the group was able to identify a number of changes that showed up in specific regions of the HIV genome in samples from the brain. Overall, the virus in the brain generally appears to be a distinct genetic lineage from that found in the blood plasma. Not surprisingly, many of the changes clustered in a region of the viral envelope protein, which is both essential for targeting the virus to cells and is in turn the most likely target for an immune response. The authors also found that the cerebro-spinal fluid contains little in the way of antibodies that recognize HIV, and suggest that the freedom from immune response in the CNS may allow HIV to pick up changes that promote its infection of neural cells.